It is common to design structural components of devices, such as, for example, aircraft structural components, to withstand predicted loads plus a safety factor or overload factor. Even with safety factors, on occasion, the structural components can be stressed beyond their ability to withstand the predicted load plus the safety factor. In aircraft structures, it is desirable to protect occupants as much as possible (e.g. by minimizing the risk of fire), even during and after catastrophic failure of structural components of the aircraft. In such cases, the components are designed to fail in a predictable manner so as to minimize both damage to the aircraft and danger to the occupants.
One practice is to use fuse pins which fail at a predictable load. A fuse pin is a pin which is used to connect two structural components. The fuse pin connects the structural components such that when the design tensile or compressive load is exceeded, shear stress will cause the pin to fail thereby releasing the two structural components from one another. Fuse pins typically work well for structural components that are primarily subjected to tension or compression loads during overload; however, for structural components in rotation at the time of an overload, failure may be difficult to control.
Another practice is to design structural components to deform during the overload condition thereby absorbing some of the energy of the overload condition. An example of this practice in the automotive industry is the use of “crumple zones” in the front of an automobile to absorb some of the energy of an impact. Similarly, in the aircraft industry, an engine nacelle may be designed to deform and absorb some vertical load in a particular scenario, such as, for example, a gear up landing, thereby protecting the fuselage from excessive vertical loads. Deformation is a good way to absorb energy, but this technique will not always result in structural components failing in a predictable manner.
The invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.